This invention relates to permanent magnet dynamoelectric machines and more specifically to high speed permanent magnet dynamoelectric machines with the permanent magnets located in the interior of the rotor.
Electric generators of alternating current are sometimes excited or magnetized by means of permanent magnets because this leads to machines of simple, robust construction having high efficiency and being free of slip rings or commutators.
It is important to obtain a sufficiently strong magnetic field in the air gap of the machine, using permanent magnets whose optimum field strength is the field strength required in the air gap. Optimum field strength is the field strength in the magnet which maximizes the stored magnetic energy per unit volume in the magnet and which therefore leads to a design in which magnet volume, weight and cost are minimized.
In addition to obtaining optimum field strength, there is a need for adequate mechanical support of the permanent magnets located in the interior of the rotor. The magnets, as well as the surrounding structures, are subjected to various systems of forces arising from thermal expansion, rotation and residual forces from the manufacturing process, such as distortions from welding.
In previous high peripheral speed permanent magnet rotor designs such as the one shown in Richter U.S. Pat. No. 4,117,360, issued Sept. 26, 1978, and assigned to the instant assignee, a composite shrink ring of magnetic and nonmagnetic pieces welded together is used to hold the magnets and the remaining rotor assembly. The pole pieces in the rotor assembly are solid pieces of magnetic material.
It is an object of the present invention to provide a rotor for a permanent magnet machine in which the magnets are not required to contribute structural strength to the rotor.
It is a further object of the present invention to provide a rotor for a permanent magnet machine in which the magnets may be easily inserted in the magnetized condition.
It is a still further object of the present invention to provide a rotor for a permanent magnet machine in which high precision assembly is achieved with minimum distortion from welding or brazing.
It is another object to provide a rotor for a permanent magnet machine which is capable of rapid disassembly and reassembly without damage.
It is yet another object of the present invention to provide a rotor for a permanent magnet machine which is suitable for manufacturing large diameter high speed machines (diameter up to about 15 inches at 3600 rpm).
It is a still further object of the present invention to provide a rotor with laminated pole pieces for a permanent magnet machine, which is suitable for use in large diameter high speed machines.